A scraper conveyor is used, for instance, in a long-wall mining operation to convey ore or coal. It comprises an upwardly open channel that normally extends horizontally parallel to the face so that a coal plow or the like can cut ore or coal from the face and deposit it in the channel. A stretch of a massive chain extends along the channel and has a succession of flights that extend transverse to the chain between the raised sides of the channel to push along the material therein.
The conveyor chain is subjected to enormous tension so that it inevitably stretches and must therefore be tightened. It is therefore standard practice to arrest the chain in the conveyor by fixing to each side of the conveyor an anchor shoe or block, securing a so-called bridge or crosspiece to a horizontal link of the chain, and then fixing the ends of the crosspiece to these blocks so that tension can be applied to the chain which is locally locked in the conveyor channel. To this end the channel sides have vertically throughgoing bores and the anchor shoes are each formed with an outer groove that fits with the upper edge of the respective side and with a vertical hole that can be aligned with the hole of the side to allow a pin to be dropped into place to fix the shoe to the respective side. Each shoe is further formed with an inwardly directed inner groove into which the respective end of the crosspiece can engage. Another vertical bore in the shoe traverses this inner groove and the ends of the crosspiece are formed with vertically throughgoing holes so that when aligned another pin can be dropped into place to fix each crosspiece end in the respective shoe.
The disadvantage of this system is that it is necessary to align the holes of the crosspieces perfectly with the inner holes of the respective shoes. Doing this is quite difficult as it is hard to move the massive chain in tiny increments accurately in order to get the necessary alignment. Thus there is normally a certain amount of forward and reverse movement until the crosspiece can be locked into the anchor shoes.